1. Field of the Invention
This invention relates to a magnetic recording powder for use as a material for magnetic recording media such as magnetic tapes and magnetic cards, and more particularly to a magnetic recording powder of this kind which has a high coercive force at room temperatures and a low Curie point.
2. Description of the Prior Art
Conventionally known magnetic recording powders of this kind include .gamma.-Fe.sub.2 O.sub.3 powders, Ba ferrite powders, RCo.sub.5 powders (R is an element selected from rare-earth elements including yttrium. Sm is mainly used as R), and Nd-Fe-B alloy powders as disclosed in Japanese Provisional Patent Publication (Kokai) No. 59-229461. The coercive force (iHc) at room temperatures and Curie point (Tc) of these conventional magnetic recording powders are shown in Table 1.
TABLE 1 ______________________________________ Kind of Magnetic Coercive Force Curie Point Recording Powder iHc (Oe) Tc (.degree.C.) ______________________________________ .gamma.-Fe.sub.2 O.sub.3 powder Appox. 400 Approx. 600 Ba Ferrite Approx. 3000 Approx. 450 Powder RCo.sub.5 Powder 10000 or more Approx. 700 Nd--Fe--B Alloy 10000 or more Approx. 320 Powder ______________________________________
Magnetic recording media such as magnetic tapes and magnetic cards are manufactured by applying magnetic recording powders over surfaces of tapes or sheets of synthetic resin. To magnetically write or erase a magnetic recording medium thus manufactured, usually the medium is heated to a temperature immediately below the Curie point of the magnetic recording powder forming the medium to have its coercive force reduced, and then the medium is subjected to magnetic writing or erasing while it has a thus reduced coercive force.
However, the aforesaid conventional magnetic recording powders have high Curie points, requiring a great deal of energy to heat to their high Curie
Many studies have been made in order to develop magnetic recording powders having low Curie points. However, a problem has been encountered that if a magnetic recording medium in general is improved to have a lower Curie point, it also has a correspondingly reduced coercive force at room temperatures. Particularly, the conventional Nd-Fe-B alloy powders have their coercive forces drastically reduced when they are finely crushed.